A manometer is an instrument used to measure the pressure of liquids and gases, typically using a column of liquid. The simple manometer used in this example consists of two vertical limbs filled with mercury (sp. gr. = 13.6) that are open to the atmosphere on one side and connected to the pipe containing oil (sp. gr. = 0.8) on the other side. The level of mercury in each limb is measured relative to a fixed reference point at the center of the pipe, which is 9 cm below the level in right limb.

In order to calculate the absolute pressure of oil in pipe, we can apply Bernoulli’s equation: P + ρgh = constant, where P is pressure, ρ is density, g is gravity constant and h is height above reference point. Since both sides are open to atmosphere, atmospheric pressure can be considered as zero so we can rewrite equation as: P +ρgh1 – ρgh2 = 0 where h1 and h2 are heights from reference points for left and right limb respectively .